Excitonic effects in the optical properties of CdSe nanowires

Using a first-principle approach beyond density functional theory we calculate the electronic and optical properties of small diameter CdSe nanowires.Our results demonstrate how some approximations commonly used in bulk systems fail at this nano-scale level and how indispensable it is to include crystal local fields and excitonic effects to predict the unique optical properties of nanowires. From our results, we then construct a simple model that describes the optical gap as a function of the diameter of the wire, that turns out to be in excellent agreement with experiments for intermediate and large diameters.Comment: submitte

Effects of thickness on the spin susceptibility of the 2D electron gas

Using available quantum Monte Carlo predictions for a strictly 2D electron gas, we have estimated the spin susceptibility of electrons in actual devices taking into account the effect of the finite transverse thickness and finding a very good agreement with experiments. A weak disorder, as found in very clean devices and/or at densities not too low, just brings about a minor enhancement of the susceptibility.Comment: 4 pages, 3 figure

DNA wrapping around MWNTs and graphene: a SERS study

In recent years, carbon nanostructure as nanotubes (CNTs) and graphene are at the centre of a significant research effort due to the strong scientific and technological interest because of their unique physical and chemical properties: large surface area, excellent thermal and electric conductivity, high electron transfer kinetics and strong mechanical strength. Recently, a great attention has been paid to the interaction of DNA with carbon-based nanostructures such as C60, multiwalled-nanotubes (MWNTs), single-walled nanotubes (SWNTs) and graphene. The development of these studies is motivated by a wide spectrum of possible use of these materials e.g. as biosensors, drug delivery agents and diagnosis tools. In this work, we applied surface-enhanced Raman spectroscopy (SERS) to the study of DNA/MWNTs and DNA/graphene systems

Caracterização florística de bancos de sementes em sistemas integrados de produção com diferentes níveis de sombreamento

O banco de sementes de plantas daninhas faz parte da dinâmica dessas espécies em áreas agrícolas, sendo resultante do manejo de plantas daninhas e dos sistemas em que se encontra. Objetivou-se com este estudo caracterizar os bancos de sementes em sistemas integrados de produção com gado leiteiro e diferentes níveis de sombreamento nos dois primeiros anos de experimento de longa duração, instalado na Embrapa Agrossilvipastoril, Sinop-MT. O experimento apresenta quatro quadrantes, constituídos por: Q1: pastagem de 1º. ano seguida por pastagem de 2º. ano; Q2: lavoura de 2º. ano seguida por pastagem 1º. ano; Q3: lavoura de 1º. ano seguida de lavoura de 2º. ano; Q4: pastagem de 2º. ano seguida de lavoura 1º. ano. Os quadrantes foram subdivididos em três níveis de sombreamento (sem eucalipto, com renques de linhas duplas de eucaliptos nas laterais da parcela e renques de linha tripla de eucalipto no interior da parcela). Fez-se coleta sistemática por conglomerados com seis amostras compostas por três subamostras na camada de 0 a 0,10 m de profundidade em cada nível de sombreamento dos quatro quadrantes do experimento. As amostras foram avaliadas em casa de vegetação e irrigadas diariamente. As plântulas emergidas foram contadas, identificadas e descartadas quinzenalmente durante três meses. O banco de sementes foi caracterizado pela importância relativa das espécies que ocorreram nos sistemas de produção. Assim, as espécies de Cyperus tendem a predominar em áreas com ausência de árvores e Eleusine indica tende a predominar em áreas sombreadas por árvores. O número de espécies de plantas daninhas tende a aumentar nos sistemas de produção avaliados e de diminuir quando ocorrem dois anos de lavoura

Participative ergonomics for the improvement of occupational health and safety in industry: a focus group-based approach

This paper introduces a participative approach to the investigation and promotion of health and safety in industry. The proposed methodology promotes the active participation of the workers in the analysis of consequences and causes of unsafe behaviours that may result in work-related musculoskeletal disorders, accidents, injuries or near-misses. The developed participative technique is the Focus Group with Workers, based on the Fault Tree Analysis method (FGW-FTA). Focus groups are conventionally used by social and behavioural researchers to understand opinions, motivations, attitudes, and mental processes that underlie people behaviours. The innovative procedure in this paper addresses researchers and safety professionals during the focus groups with the workers for the identification of critical risk factors in the workplace. The result is a structured analysis, operated by and with the workers, for the identification of consequences and causes of unsafe behaviours. Finally, the developed methodology addresses the definition of a set of preventive and protective measures, and corrective actions for the improvement of health and safety in the workplace. An experimental study in an Italian boiler manufacturer describes the proposed methodology and the results of the focus groups with the workers. An evaluation questionnaire was elaborated to investigate the workers’ knowledge on occupational health and safety. A second questionnaire was developed to understand the workers’ perception on occupational risks. Each participant was invited to fill in both the questionnaires before and after the focus groups with the workers. The results of the study proved the effectiveness of the developed methodology in improving workers knowledge and perceptions on occupational health and safety

Knowledge Acquisition by Networks of Interacting Agents in the Presence of Observation Errors

In this work we investigate knowledge acquisition as performed by multiple agents interacting as they infer, under the presence of observation errors, respective models of a complex system. We focus the specific case in which, at each time step, each agent takes into account its current observation as well as the average of the models of its neighbors. The agents are connected by a network of interaction of Erd\H{o}s-Renyi or Barabasi-Albert type. First we investigate situations in which one of the agents has a different probability of observation error (higher or lower). It is shown that the influence of this special agent over the quality of the models inferred by the rest of the network can be substantial, varying linearly with the respective degree of the agent with different estimation error. In case the degree of this agent is taken as a respective fitness parameter, the effect of the different estimation error is even more pronounced, becoming superlinear. To complement our analysis, we provide the analytical solution of the overall behavior of the system. We also investigate the knowledge acquisition dynamic when the agents are grouped into communities. We verify that the inclusion of edges between agents (within a community) having higher probability of observation error promotes the loss of quality in the estimation of the agents in the other communities.Comment: 10 pages, 7 figures. A working manuscrip

Grapevine yellows diseases in Spain: eight years survey of disease spread and molecular characterization of phytoplasmas involved.

Among grapevine yellows phytoplasma diseases in Europe, flavescence dor\ue9e (FD) is the most devastating and in the last decade has reached Spanish vineyards, mainly in Catalonia. An eight-year survey was carried out in the areas where the disease has spread (Alt Empord\ue0, Catalonia, Northern Spain) and in the remaining vine-growing areas of Catalonia. Sequence analyses of a portion of the 16S-23S ribosomal DNA cistron, from selected grapevine samples from Catalonia, showed that the phytoplasmas involved in grapevine yellows belong to 16S ribosomal subgroups V-D (flavescence dor\ue9e, FD) and XII-A (bois noir, BN). A set of Spanish FD isolates collected during these years were further studied by RFLP analyses of the 16S-23S ribosomal DNA fragment, as well as the rpS3 and SecY genes. All the FD phytoplasma strains studied were related to phytoplasmas belonging to ribosomal protein subgroup rp-E

Caracterização florística de bancos de sementes em sistemas solteiros e integrados de produção

Objetivou-se com este estudo caracterizar a dinâmica de espécies de plantas daninhas em banco de semente de sistemas solteiros e integrados de produção em experimento de longa duração instalado na Embrapa Agrossilvipastoril em Sinop-MT. O delineamento experimental foi o de blocos ao acaso com quatro repetições e dez tratamentos [1) floresta solteira; 2) sucessão soja/consórcio milho-pastagem; 3) pastagem solteira; 4) sistema integração lavoura-pecuária (ILP) com dois anos de lavoura, seguidos de dois anos de pastagem; 5) sistema integração pecuária-lavoura (IPL), com dois anos de pastagem, seguidos de dois anos de lavoura; 6) sistema lavoura-floresta (LF), com floresta e lavoura nas entrelinhas; 7) sistema pecuária-floresta (PF), com floresta e pastagem nas entrelinhas; 8) sistema ILPF, com floresta e quatro anos de lavoura, seguidos de quatro anos de pastagem nas entrelinhas ?3?; 9) sistema ILPF, com floresta e quatro anos de pastagem, seguidos de quatro anos de lavoura nas entrelinhas; 10) sistema ILPF, com floresta e, nas entrelinhas, sucessão soja-consórcio milho-pastagem, com colheita do milho e estabelecimento do pasto no inverno para pastejo animal (recria/terminação)]. Fez-se coleta sistemática por conglomerados com quatro amostras compostas por cinco subamostras na primeira safra (2012/2013) e duas subamostras na segunda safra (2013/2014) na camada de 0 a 0,10 m. As amostras foram avaliadas em casa de vegetação e irrigadas diariamente. As plântulas emergidas foram contadas, identificadas e descartadas quinzenalmente durante três meses. Eleusine indica foi a principal espécie em todos os sistemas de produção no 1º. levantamento e continuou a ser a principal espécie em praticamente todos os sistemas de produção na safra seguinte. Hyptis brevipes foi a segunda principal espécie em sete dos 10 sistemas de produção na primeira safra e Digitaria horizontalis foi a segunda principal espécie em seis dos 10 sistemas de produção na segunda. A estrutura florística do banco de sementes é modificada no tempo em sistemas solteiros e integrados de produção. Há aumento no número de espécies em praticamente todos os sistemas de produção, à exceção sistema pecuária-floresta (PF), com floresta e pastagem nas entrelinhas